[petsc-users] ghost values

[Matthew Knepley]

On Tue, Apr 14, 2015 at 6:15 PM, Gideon Simpson <gideon.simpson at gmail.com>
wrote:

> Other than zeroing things out, is there any substantive difference between
> DMCreateLocalVector and DMGetLocalVector?
>

The Get version caches vectors, so you are not continually
creating/destroying

   Matt


> -gideon
>
> > On Apr 14, 2015, at 7:02 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >
> >  When PETSc vectors are created initially they always have 0 everywhere.
> So if you use DMCreateLocalVector() it will have zero in all those ghost
> places (as well as everywhere else).
> >
> >   But if you use DMGetLocalVector() it returns vectors that maybe dirty
> so you need to fill in any locations you want to have a known value with
> that known value. Or call VecSet() to clear the entire vector.
> >
> >  Barry
> >
> >> On Apr 14, 2015, at 5:52 PM, Gideon Simpson <gideon.simpson at gmail.com>
> wrote:
> >>
> >> If i use the DM_BOUNDARY_GHOSTED flag in the creation of a DMDA array,
> are the ghosted values automatically set to zero, or should they be
> manually set to zero if that’s the desired ghost value?
> >>
> >> -gideon
> >>
> >
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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